Energy of a Wave & the Photoelectric Effect: Is My Statement Correct?

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Discussion Overview

The discussion revolves around the relationship between the energy of electromagnetic waves and the photoelectric effect, examining classical electrodynamics and the implications of quantization. Participants explore whether classical theories adequately explain the photoelectric effect and the role of intensity and amplitude in defining wave energy.

Discussion Character

  • Debate/contested
  • Technical explanation
  • Conceptual clarification

Main Points Raised

  • Some participants assert that in classical electrodynamics, the energy of a wave is proportional to its intensity, while others clarify that intensity is defined as the power per unit area and is proportional to the square of the amplitude of the wave.
  • There is a contention regarding whether classical electrodynamics can adequately explain the photoelectric effect, with some arguing that it cannot, while others suggest that classical electromagnetic radiation can still account for the effect under certain conditions.
  • Some participants propose that quantization of electromagnetic radiation is consistent with the photoelectric effect but not necessary for its explanation, while others reference Einstein's role in proposing quantization to explain the phenomenon.
  • A participant questions why intense white light does not lead to electron emission, prompting references to external texts and videos for further clarification.
  • Another participant expresses uncertainty about the relationship between intensity and energy in a quantized electromagnetic field, suggesting that intensity remains proportional to the average energy of the field.
  • There is a discussion about whether the light source needs to be quantized, with a query about the necessity of ultraviolet wavelengths to exceed the work function of the material for electron emission.

Areas of Agreement / Disagreement

Participants do not reach a consensus on the adequacy of classical theories to explain the photoelectric effect, and multiple competing views remain regarding the necessity of quantization and the definitions of intensity and energy.

Contextual Notes

Limitations include varying definitions of intensity and energy, as well as unresolved questions about the conditions under which classical theories may or may not apply to the photoelectric effect.

Sandeep T S
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In classical electrodynamics energy of a wave is proportional to its intensity , this theory fails when Hertz did experiment on photoelectric effect. Is my statement is correct? If not correct me.
 
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Sandeep T S said:
In classical electrodynamics energy of a wave is proportional to its intensity

What do you mean by "intensity"? The correct mathematical statement is that the energy of a classical EM wave is proportional to the square of its amplitude.

Sandeep T S said:
this theory fails when Hertz did experiment on photoelectric effect

What theory? Classical electrodynamics? Yes, the observed photoelectric effect cannot be explained by classical electrodynamics. However, that has nothing to do with the classical formula for the energy carried by an EM wave.
 
Sandeep T S said:
In classical electrodynamics energy of a wave is proportional to its intensity , this theory fails when Hertz did experiment on photoelectric effect. Is my statement is correct? If not correct me.

Quantization of the electromagnetic is consistent with the photoelectric effect, but it is not necessary to explain the photoelectric effect, i.e., the photoelectric effect can be explained by a classical electromagnetic radiation incident on a photomaterial. Of course, the photoelectric effect can be explained by quantized electromagnetic radiation incident on a photomaterial.

Both situations are treated quantitatively in the interesting book "Quantum Mechanics: Theory and Experiment" by Mark Beck.
 
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George Jones said:
Quantization of the electromagnetic is consistent with the photoelectric effect, but it is not necessary to explain the photoelectric effect, .
But I thought Einstein proposed quantisatiion to explain the effect. Why does intense white light not create electron emission?
 
tech99 said:
But I thought Einstein proposed quantisatiion to explain the effect. Why does intense white light not create electron emission?

This is explained in the text that I referenced, which probably is unavailable to you. See also the video below (between times 27:30 and 30:23), by Alain Aspect, who, in my opinion, should be a Nobel Laureate.

 
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Sandeep T S said:
In classical electrodynamics energy of a wave is proportional to its intensity , this theory fails when Hertz did experiment on photoelectric effect. Is my statement is correct? If not correct me.

As George Jones already said, one may use a classical electromagnetic field in dealing with the photoelectric effect, and since the definition of intensity is independent of whether you treat the rest of the system as quantum or not, intensity is still proportional to the energy of an electromagnetic wave.

With that said, given the definition of intensity, I am fairly certain that even with a fully quantized electromagnetic field it would still be proportional to the (average/time averaged) energy of the field. But I'm happy to be corrected if I'm wrong on this point.

PeterDonis said:
What do you mean by "intensity"? The correct mathematical statement is that the energy of a classical EM wave is proportional to the square of its amplitude.

Intensity is the power per unit area. For an electromagnetic wave. It is also proportional to the square of the amplitude of the electric field.
 
George Jones said:
This is explained in the text that I referenced, which probably is unavailable to you. See also the video below (between times 27:30 and 30:23), by Alain Aspect, who, in my opinion, should be a Nobel Laureate.

Thank you very much for this fantastic lecture. Are we saying that the light source need not be quantised, but the wavelength must be ultra violet so that the wave energy exceeds the work function of the material?
 

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